aic: Fix decoding files with odd dimensions

aic: Fix decoding files with odd dimensions

Normally the aic decoder finds the proper slice combination (multiple of
some number less than 32) but in case of odd width, it resorts to the
default values, which were actually swapped.
The number of slices is modified to account for such odd width cases.

CC: libav-stable@libav.org
(cherry picked from commit e878ec0d47cd6228c367b2f3128b76d7523f7255)
Signed-off-by: Luca Barbato <lu_zero@gentoo.org>